Vehicle anti-block systems frequently utilize inductive transducers which, at low vehicle speed and due to the comparatively large air-gap in the magnetic system provide sine-like output signal of low amplitude. The output voltage derived from such transducers is analyzed in circuits, including threshold switches. This output voltage, for example, should be converted into square-wave signals of 1:1 duty cycle, that is, approximately equal space between pulses and gaps for subsequent signal processing in a logic circuit. The signal processing apparatus usually uses bipolar planar integrated circuits. The signal-to-noise ratio to the input of the logic circuits should be as high as possible. Accordingly, there is a demand for threshold switches which may include threshold switch circuits which are essentially temperature-stable, accurate with respect to reference voltage levels, for example a ground or chassis voltage level, and which is symmetrical with respect to response voltages, while, additionally, including some hysteresis.
Threshold switches which can be used in vehicle anti-block circuits frequently utilize comparators with integrated circuit (IC) operational amplifiers which have a positive feedback circuit including at least a resistor which leads from the output of the circuit to the direct input thereof in order to provide for hysteresis. Various circuits are known to generate a fixed reference voltage, for example bandgap voltage circuits.